Microporous polymeric foams made with silicon or germanium based monomers

ABSTRACT

Disclosed are polymeric foam materials obtained using monomers based on silicon and/or germination. The copolymerization of silicon- or germanium-based monomers provide foams that have low glass transition temperatures and low densities. These foams also exhibit relatively high yield stress values, which make the foams suitable for absorption of fluids, particularly aqueous fluids such as urine and menses (when the foams are rendered hydrophilic). The foams have a variety of other uses, including insulation applications.

This is a 371 of PCT/US97/22939, filed on Dec. 5, 1997, which is acontinuation-in-part of provisional application Ser. No. 60/034,156,filed on Dec. 30, 1996.

FIELD OF THE INVENTION

This application relates to microporous, open-celled polymeric foamsmade using monomers based on silicon or germanium.

BACKGROUND OF THE INVENTION

The development of microporous foams has been the subject of substantialcommercial interest. Such foams have found utility in variousapplications, such as thermal, acoustic, electrical, and mechanical(e.g., for cushioning) insulators, absorbent materials, filters,membranes, carriers for inks, dyes, lubricants, and lotions, makingitems buoyant, and the like. References describing such uses andproperties of foams include Oertel, G. "Polyurethane Handbook" HanserPublishers, Munich, 1985, and Gibson, L. J.; Ashby, M. F. "CellularSolids Structure and Properties" Pergamon Press, Oxford, 1988. The term"insulator" refers to any material which reduces the transfer of energyfrom one location to another. The term "absorbent" refers to materialswhich imbide and hold or distribute fluids, usually liquids, an examplebeing a sponge. The term "filter" refers to materials which pass afluid, either gas or liquid, while retaining impurities within thematerial by size exclusion. Other uses for foams are generally obviousto one skilled in the art.

For many uses, composite and generally conflicting requirements areplaced on the foam itself. These may include (1) low density, (2)flexibility, (3) strength (compressive and tensile), (4) openness, and(5) control of morphology. Low density foams are more efficient sincemost uses require a certain volume and a low density foam will imposeless mass to meet this objective. Flexible foams are typically generatedby maintaining a relatively low glass transition temperature ("Tg") ofthe foam. Strength is a parameter which is inevitably sacrificed toachieve either lower Tg or lower density. Strength can be generatedeffectively by including crosslinking agents which link the polymericchains of the foam together in a fashion which confers a degree ofresistance to deformation and the ability to recover from deformation,e.g., elasticity. Openness and morphology are controlled principally bythe method of foam formation and curing.

Accordingly, it would be desirable to be able to make an open-celled,high surface area polymeric foam material that: (1) has the lowestdensity consistent with the other requirements imposed on the foam; (2)is flexible; (3) is strong; (4) has a generally open-celled structure;and (5) can be manufactured so as to control the size of cells producedwithin the foam.

SUMMARY OF THE INVENTION

The present invention relates to polymeric foams comprising comonomersbased on silicon and/or germanium. The term "comonomer" is used hereinto denote that these required comonomers are generally to be used withother comonomers which may or may not contain silicon and/or germanium.These polymeric foams are preferably prepared by polymerization ofcertain water-in-oil emulsions having a relatively high ratio of waterphase to oil phase, commonly known in the art as high internal phaseemulsions, or "HIPEs". As used herein, polymeric foam materials whichresult from the polymerization of such emulsions are referred tohereafter as "HIPE foams." The HIPE foam materials of the presentinvention comprise a generally flexible, semi-flexible, or rigidnonionic polymeric foam structure of interconnected open-cells.Comonomers used to form HIPEs generally must be relatively insoluble inthe aqueous phase of the emulsion.

The polymeric foam structures that are derived from HIPEs comprise atleast about 5%, based on the weight of the foam, of one or morecomonomer(s) selected from the group consisting of silicon-containingcomonomers, germanium-containing comonomers, and mixtures thereof.

Preferably, the foams of the present invention will have:

A) a density of less than about 0.10 g/cc;

B) a glass transition temperature (Tg) of between about -40° and 90° C.;and

C) a yield stress value of at least about 0.25 psi.

The present invention relates to foams prepared via polymerization of aHIPE comprising a discontinuous water phase and a continuous oil phasewherein the ratio of water to oil is at least about 10:1. The waterphase generally contains an electrolyte and a water soluble initiator.The oil phase generally consists of substantially water-insolublemonomers polymerizeable by free radicals, including at least onecomonomer which contains silicon and/or germanium, an emulsifier, andother optional ingredients defined below. The monomers which containsilicon and/or germanium are selected so as to confer the propertiesdesired in the resulting polymeric foam, e.g. low density, a glasstransition (Tg) between about -40° and 90° C., mechanical integritysufficient for the intended end use, and an open-celled, microporousmorphology.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 of the drawings is a photomicrograph (250× magnification) of acut section of a representative polymeric foam of the present inventionmade from a HIPE having a 60:1 water-to-oil weight ratio and formed at55° C., where the monomer component consisted of a 55:33:12 weight ratioof 2-ethylhexyl acrylate (EHA):divinyl benzene (about 40% DVB and about60% ethyl styrene):tetrakis(3-methacryloxyethoxy)silane, and where 10%(by weight of the oil phase) of diglycerol monooleate (DGMO) emulsifierwas used.

FIG. 2 of the drawings is a photomicrograph (1000× magnification) of thefoam of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

I. Polymeric Foams Containing Silicon and/or Germanium

Polymeric foams of the present invention are comprised of specificcombinations of monomers which to a large extent control the ultimateproperties of the foam. The types of monomers used fall into thefollowing three general categories: (1) monomers which help maintain adesirable Tg in the resulting polymer, (2) monomers which help confer"toughness" to the resulting polymer, herein referred to as "tougheningmonomers", and (3) monomers which have di-, tri-, tetra-, and higherfunctionality useful in conferring crosslinks within the resultingpolymer, herein referred to as crosslinkers. These crosslinks areparticularly critical in achieving the desired comprehensive strength ormodulus and/or elasticity which is required for many foam applications.Applicants have discovered that, surprisingly, monomers which containsilicon and/or germanium are particularly useful in areas (1) and (3)above. For example, a comonomer such as(3-acryloxypropyl)methylbis(trimethylsiloxy)silane (referred tohereinafter as APMTS) forms polymers which have desirably low Tgs. Asanother example, a crosslinker such astetrakis(2-methacryloxyethoxy)silane (referred to hereinafter as TKMES)forms polymers which are effectively crosslinked so as to have desirablecompressive strength and elasticity without increasing the Tg of theresulting polymeric foam to an undesirable degree. The general class ofsuch compounds is described more completely hereinafter, though thesetwo are presented as being generally illustrative, nonrestrictiveexamples of the invention. It is understood that both of theserepresentative examples are used as comonomers with other comonomers toconfer the properties desired in the ultimate foam.

The ability of these silicon and/or germanium based comonomers to conferthe desired strength without increasing the Tg undesirably is thought torelate to the molecular flexibility associated with bonds attached tothe Si and/or Ge atom. This flexibility is seen in polysiloxanes whichhave very low Tgs. In contrast, comonomers which confer strength whilelacking sufficient molecular flexibility tend to increase Tg. Examplesinclude divinyl benzene, a crosslinker wherein higher levels mayincrease the strength of the polymer while also increasing the Tg. Tg isan important criterion in the use of any polymer. While in some uses arelatively high Tg may be desired, in general this is more easilyaccomplished than achieving a corresponding low Tg in a polymer withoutsacrificing other properties such as strength to an undesirable degree.Applicants have found that the comonomers used in the present inventionare particularly useful in maintaining a comparatively low Tg while alsoconferring sufficient strength for many uses in the final product.

The polymers that constitute the present foams comprise from about 0.5%to about 30% elemental silicon or germanium, or a combination of thetwo. Preferably, the polymer will comprise from about 1% to about 15%,more preferably from about 2% to about 10%, of these elements. While thefoams may be described in terms of their elemental silicon/germaniumcontent, it is understood that these elements are covalently bound toother polymerizeable groups and are introduced into the foam's polymerin the form of silicon/germanium-containing comonomers.

II. General Foam Characteristics

The polymeric foams of the present invention are relatively open-celled.This means the individual cells of the foam are in complete,unobstructed communication with adjoining cells. The cells in suchsubstantially open-celled foam structures have intercellular openings or"windows" connecting one cell to another within the foam structure.

These substantially open-celled foam structures will generally have areticulated character with the individual cells being defined by aplurality of mutually connected, three dimensionally branched webs. Thestrands of polymeric material making up these branched webs can bereferred to as "struts." Open-celled foams having a typical strut-typestructure are shown by way of example in the photomicrographs of FIGS. 1and 2. As used herein, a foam material is "open-celled" if at least 80%of the cells in the foam structure that are at least 1 μm in size are inopen communication with at lest one adjacent cell.

These polymeric foams may generally be hydrophobic to inhibit thepassage of aqueous fluids through the foam, or hydrophilic to encourageimbibition of aqueous fluids into the foam. The hydrophobic/hydrophilicproperties of the internal surfaces of the foam structures arecontrolled by post-polymerization foam treatment procedures. As usedherein, the term "hydrophilic" is used to refer to surfaces that arewettable by aqueous fluids deposited thereon. Hydrophilicity andwettability are typically defined in terms of contact angle and thesurface tension of the fluids and solid surfaces involved. This isdiscussed in detail in the American Chemical Society publicationentitled Contact Angle, Wettability and Adhesion, edited by Robert F.Gould (Copyright 1964), which is hereby incorporated herein byreference. A surface is said to be wetted by a fluid (i.e., hydrophilic)when either the contact angle between the fluid and the surface is lessthan 90°, or when the fluid tends to spread spontaneously across thesurface, both conditions normally co-existing. Conversely, a surface isconsidered to be "hydrophobic" if the contact angle is greater than 90°and the fluid does not spread spontaneously across the surface.

The foams used according to the present invention are readily optimizedso as to confer the properties desired in each specific application. Asexamples, these foams may be microcellular (<10 μm) up through moderatecell diameters (ca. 150 μm); low density (0.10 g/cc) to very low density(0.004 g/cc); rigid to flexible (corresponding, high Tg to low(subambient) Tg); and strong to weak. The foams may be provided ascontinuous sheets, rigid thick boards, particulates of various sizes,specific shapes, etc., as required by their end use. However optimized,these foams avoid some of the deficiencies associated with the foammethods described hereinabove. That is, they generally contain little orno nitrogen or sulfur so that burning produces no unusually noxiousgases, require no CFC or volatile organic compound ("VOC") materialsduring manufacture, are generally photostable, are producible readily inlarge quantities with reasonable economics as either slabstock, rollstock, particulate foam, and the like.

A. Glass Transition Temperature

A key parameter of the foams of the present invention is their glasstransition temperature (Tg). The Tg represents the midpoint of thetransition between the glassy and rubbery states of the polymer. Foamsthat have a Tg higher than the temperature of use can be very strong butcan also be very rigid and potentially prone to fracture. Such foamsalso typically take a long time to recover to the expanded state afterhaving been stored in the compressed state for prolonged periods. Thoughthe end use of a particular foam is an important factor when determiningthe desired Tg of the foam, preferred are foams having a Tg of fromabout 15° to about 50° C. More preferred are foams having a Tg of fromabout 20° to about 40° C. The silicon and/or germanium containingcomonomers described hereinafter are particularly useful in developinglow Tg polymers. The method for determining Tg by Dynamic MechanicalAnalysis (DMA) is described in the TEST METHODS section infra.

B. Foam Density

Another important property of the foams of the present invention istheir density. "Foam density" (i.e., in grams of foam per cubiccentimeter of foam volume in air) is specified herein on a dry basis,unless otherwise indicated. Any suitable gravimetric procedure that willprovide a determination of mass of solid foam material per unit volumeof foam structure can be used to measure foam density. For example, anASTM gravimetric procedure described more fully in the TEST METHODSsection of U.S. Pat. No. 5,387,207 (Dyer et al.), issued Feb. 7, 1995(incorporated by reference herein) is one method that can be employedfor density determination. While foams can be made with virtually anydensity ranging from below that of air to just less than the bulkdensity of the polymer from which it is made, the foams of the presentinvention are most useful when they have a dry density in the expandedstate of less than about 0.10 g/cc, preferably between about 0.08 andabout 0.004 g/cc, more preferably between about 0.04 and 0.01 g/cc, andmost preferably about 0.02 g/cc.

C. Cell Size

Foam cells, and especially cells that are formed by polymerizing amonomer-containing oil phase that surrounds relatively monomer-freewater-phase droplets, will frequently be substantially spherical inshape. The size or "diameter" of such spherical cells is a commonly usedparameter for characterizing foams in general. Since cells in a givensample of polymeric foam will not necessarily be of approximately thesame size, an average cell size, i.e., average cell diameter, will oftenbe specified.

A number of techniques are available for determining the average cellsize of foams. The most useful technique, however, for determining cellsize in foams involves a simple measurement based on the scanningelectron photomicrograph of a foam sample. FIG. 1, for example, shows atypical HIPE foam structure according to the present invention.Superimposed on the photomicrograph is a scale representing a dimensionof 100 μm. Such a scale can be used to determine average cell size viaan image analysis procedure.

The cell size measurements given herein are based on the number averagecell size of the foam, e.g., as shown in FIG. 1. The foams of thepresent invention will preferably have a number average cell size of notmore than about 150 μm, more preferably from about 10 to 100 μm, andmost preferably from about 15 μm to 35 μm. As with other foamcharacteristics, the preferred average cell size for a given foam willbe dictated in-part by its anticipated end use.

D. Specific Surface Area

Another important parameter of the foams is their specific surface area,which is determined by both the dimensions of the cellular units in thefoam and by the density of the polymer, and is thus a way of quantifyingthe total amount of solid surface provided by the foam. Specific surfacearea is determined by measuring the amount of capillary uptake of a lowsurface tension liquid (e.g., ethanol) which occurs within a foam sampleof known mass and dimensions. A detailed description of such a procedurefor determining foam specific surface area via the capillary suctionmethod is set forth in the TEST METHODS section of U.S. Pat. No.5,387,207 (Dyer et al.), issued Feb. 7, 1995, which is incorporatedherein by reference. Other similar tests for determining specificsurface area can be used with the present foams.

The foams of the present invention have a specific surface area of atleast about 0.01 m² /cc, preferably at least about 0.025 m² /cc.

E. Yield Stress

Yield stress is determined in a stress-strain experiment conducted onthe foam at a specified temperature and rate of strain (in compressionmode). The yield stress is the stress at the transition from the linearelastic region to the plateau region of the stress-strain curve. Yieldstress is indicative of the general strength properties of the polymericfoam at the temperature of interest. For many applications, higher yieldstress values are desirable at a given foam density and Tg. The foams ofthe present invention will preferably have a yield stress value of atleast about 0.25 psi, preferably at least about 0.5 psi.

III. Foam Uses

The polymeric foams of the present invention will have numerous enduses. For example, the foams may be prepared to be absorbent materials,particularly for aqueous based fluids such as urine and menses. Suchfoams will be prepared to have the structural characteristics similar tothe HIPE-derived foams described in, e.g., copending U.S. patentapplication Ser. No. 08/563,866 (DesMarais et al., filed Nov. 29, 1995);copending U.S. patent application Ser. No. 08/542,497 (Dyer et al.,filed Oct. 13, 1995); U.S. Pat. No. 5,387,207 (Dyer et al., issued Feb.7, 1995); U.S. Pat. No. 5,550,167 (DesMarais, issued Aug. 27, 1996); andU.S. Pat. No. 5,563,179 (DesMarais et al., issued Oct. 8, 1996); each ofwhich is incorporated by reference herein. Such absorbent foams may beincluded in absorbent articles such as infant diapers, femanine hygienearticles (e.g., tampons, catamenial pads), adult incontinence articles,and the like, such as those described in the aforementioned copendingpatent applications and issued patents. The foams may also be preparedso as to be useful as insulators. Such foams will have structuralcharacteristics (e.g., cell size, density, Tg) similar to the foamsdescribed in copending U.S. patent application Ser. No. 08/472,447 (Dyeret al., filed Jun. 7, 1995) and copending U.S. patent application Ser.No. 08/484,727 (DesMarais et al., filed Jun. 7, 1995, both of which areincorporated by reference herein. The polymeric foams may also be usedfor filters of fluids (liquid or gas), to remove impurities. Other usesfor foams include membranes, carriers for inks, dyes, lubricants,lotions, making items buoyant, and other uses generally obvious to oneskilled in the art.

III. Preparation of Polymeric Foams From HIPEs Using Monomers ContainingSilicon and/or Germanium

A. In General

Polymeric foams of the present invention are preferably prepared bypolymerization of HIPEs. The relative amounts of the water and oilphases used to form the HIPEs are, among many other parameters,important in determining the structural, mechanical and performanceproperties of the resulting polymeric foams. In particular, the ratio ofwater to oil in the emulsion can influence the density, cell size, andspecific surface area of the foam and dimensions of the struts that formthe foam. The emulsions used to prepare the HIPE foams will generallyhave a volume to weight ratio of water phase to oil phase of at leastabout 10:1, preferably from about 12.5:1 to about 250:1, more preferablyfrom about 25:1 to about 75:1, and most preferably about 50:1.

The process for obtaining these foams comprises the steps of:

(A) forming a water-in-oil emulsion under low shear mixing from:

(1) an oil phase comprising:

(a) from about 80% to about 98% by weight of a monomer component capableof forming a copolymer having a Tg value of from about 40° C. to about90° C., said monomer component comprising:

(i) at least about 5% by weight of a material selected from the groupconsisting of one or more comonomers containing silicon, one or morecomonomers containing germanium, and mixtures thereof;

(ii) from about 0% to about 70% by weight of a substantiallywater-insoluble, monofunctional monomer capable of forming a homopolymerhaving a Tg of about 40° C. or less;

(iii) from about 0% to about 70% by weight of a substantiallywater-insoluble, monofunctional comonomer capable of imparting toughnessabout equivalent to that provided by styrene;

(iv) from about 0% to about 50% of a first substantiallywater-insoluble, polyfunctional crosslinking agent selected from thegroup consisting of divinyl benzene and analogs thereof; and

(v) from about 0% to about 15% of a second substantiallywater-insoluble, polyfunctional crosslinking agent selected from thegroup consisting of diacrylates and dimethacrylates of diols and analogsthereof; and

(b) from about 2% to about 20% by weight of an emulsifier componentwhich is soluble in the oil phase and which is suitable for forming astable water-in-oil emulsion;

(2) a water phase comprising from about 0.1% to about 20% by weight of awater-soluble electrolyte; and

(3) a volume to weight ratio of water phase to oil phase of at leastabout 10:1; and

(B) polymerizing the monomer component in the oil phase of thewater-in-oil emulsion to form the polymeric foam material.

The polymeric foam material can be subsequently iteratively washed anddewatered to provide a dry, hydrophobic foam. Alternatively, the foammay be rendered hydrophilic by appropriate surface treatment with any ofa number of hydrophilizing agents, including calcium chloride andsimilar salts, residual emulsifiers used for stabilizing the HIPE, andother wetting agents well known to those skilled in the art.Hydrophilizing treatments are described in, e.g., U.S. Pat. No.5,387,207 (Dyer et al., issued Feb. 7, 1995) (see especially column 22to column 24), which is incorporated herein by reference.

These foams may be shaped as desired. Typically, this shaping willcomprise slicing into relatively thin sheets. These sheets mayoptionally be compressed, e.g. continuously through pressure nips, intoa thin state and wound into rolls. Compressible sheets will retain theirrelatively thin compressed state until unwound, applied as desired, andeither heated above their activation temperature (usually about the Tgof the polymer) or allowed to stand for a relatively long period oftime, e.g. several weeks or months, depending on the ambienttemperature, as described in copending U.S. patent application Ser. No.08/484,727 (DesMarais et al., filed Jun. 7, 1995). Alteratively, theshapes may be conferred by the shape of the vessel in which the HIPE iscured so as to form the polymeric foam material. Alternatively, thecured foam may be diced, shredded, ground, or otherwise comminuted intosmall particulate pieces for further use.

1. Oil Phase Components

The continuous oil phase of the HIPE comprises comonomers that arepolymerized to form the solid foam structure. This monomer component isformulated to be capable of forming a copolymer having a Tg of fromabout -40° to about 90° C., and preferably from about 15° to about 50°C., more preferably from about 20° to about 40° C. (The method fordetermining Tg by Dynamic Mechanical Analysis (DMA) is described in theTEST METHODS section infra.) This monomer component includes at leastone of a comonomer, at a level of at least about 5%, that containssilicon and/or germanium. Preferably, the monomer component will includefrom about 8% to about 50%, more preferably from about 10% to about 30%,of a comonomer(s) containing silicon and/or germanium. Levels of suchcomonomers lower than about 5% are found to induce minimally measurablechanges in the foam properties. This monomer component may furtherinclude: (a) at least one monofunctional comonomer whose atacticamorphous homopolymer has a Tg of about 40° C. or lower (see Brandup,J.; Immergut, E. H. "Polymer Handbook", 2nd Ed., Wiley-Interscience, NewYork, N.Y., 1975, III-139.), described hereinafter as a "Tg loweringmonomer"; (b) at least one monofunctional comonomer to improve thetoughness or tear resistance of the foam, described hereinafter as a"toughening monomer"; (c) a first polyfunctional crosslinking agent;and/or (d) optionally a second polyfunctional crosslinking agent. Thecomonomers described above in section (a), (b), and (c) may also containsilicon and/or germanium to satisfy the level requirements for theseelements in the formulation. The selection of particular types andamounts of monofunctional monomer(s) and comonomer(s) and polyfunctionalcross-linking agent(s) can be important to the realization of absorbentHIPE foams having the desired combination of structure, and mechanicalproperties which render such materials suitable for use in the inventionherein.

The monofunctional comonomer components which contain silicon and/orgermanium include myriad types. These can include comonomers designed toserve as Tg lowering monomers, as defined above. Examples generallyinclude monomers having at least one pendant group which is reactive infree radical polymerizations. Nonlimiting examples of such pendantgroups include acrylates, methacrylates, acrylamides, methacrylamides,styryls, dienes, vinyl sulfones, and the like. Such pendant groups arewell known to those skilled in the art. Attached to these pendant groupswill be a moiety containing at least one silicon and/or germanium atomappropriately functionalized. Nonlimiting examples of these moietiesinclude dimethylsiloxanes, germanoxanes, silanes, and germanes.Preferred examples are silicon-containing Tg lowering monomers whichcontain di- and trisiloxane moieties, for example, the groups --Si(CH₃)₂--)--O--Si(CH₃)₂ -- and --Si(CH₃)₂ --)--O--Si(CH₃)₂ --O--Si(CH₃)₂ --.These moieties provide an exceptionally flexible side chain on thependant reactive group which, after polymerization, induces a strong Tglowering effect on a weight basis. It has been found by experiment thatat least about 5% of these monomers must be used to exert the desiredinfluence. Since these monomers typically contain between about 10% andabout 40% elemental silicon and/or germanium, the amount of elementalsilicon and/or germanium in the formulation typically will be at leastabout 0.5%. The upper range in the amount of silicon and/or germaniumused in the formulation is governed by the maximum amount of suchcomonomers that can be used, which is 100% times the maximum level ofsilicon and/or germanium possible in the comonomer while retaining thereactive pendant group, which is about 50% in the case of trimethylvinylgermane. Specific nonlimiting examples of monomers include(3-acryloxypropyl)-methylbis-(trimethylsiloxy)silane, allyltriisopropylsilane, allyltriphenyl silane, bis(trimethylsilyl)itaconate,p-(t-butyldimethylsiloxy)styrene, methacrylamido-propyltriethoxysilane,methacryloxyethoxytrimethylsilane,(methacryloxymethyl)-dimethylethoxysilane, methacryloxytrimethyl silane,(2,4-pentadienyl)trimethylsilane, styrylethyltrimethoxysilane,3-(N-styrylmethyl-2-aminoethylamino)propyltrimethoxy-silanehydrochloride, (m,p-vinylbenzyloxy)trimethylsilane, vinyltrimethylsilane, vinyldimethylethyl silane, vinylpentamethyldisiloxane, vinyltrifluoromethyldimethyl silane, vinyltris(trimethylsiloxy)silane, andvinyltriethyl germane. While each of these examples will vary in theirpropensity to serve as a Tg lowering monomer, each may find specificadvantage in achieving a specific Tg for a polymeric foam needed for aparticular end use.

The monomer component may include one or more other Tg loweringmonofunctional monomers that do not contain silicon and/or germaniumthat tend to impart rubber-like properties to the resulting polymericfoam structure. Such monomers can produce high molecular weight (greaterthan 10,000) atactic amorphous homopolymers having Tgs of about 40° C.or lower. Monomers of this type include, for example, the C₄ -C₁₄ alkylacrylates such as butyl acrylate, hexyl acrylate, octyl acrylate,2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, dodecyl (lauryl)acrylate, isodecyl acrylate, tetradecyl acrylate; aryl and alkarylacrylates such as benzyl acrylate and nonylphenyl acrylate; the C₆ -C₁₆alkyl methacrylates such as hexyl methacrylate, octyl methacrylate,nonyl methacrylate decyl methacrylate, isodecyl methacrylate, dodecyl(lauryl) methacrylate, and tetradecyl methacrylate; acrylamides such asN-octadecyl acrylamide; C₄ -C₁₂ alkyl styrenes such as p-n-octylstyrene;and combinations of such monomers. Of these monomers, isodecyl acrylate,dodecyl acrylate and 2-ethylhexyl acrylate are the most preferred. Thesemonofunctional monomer(s) will generally comprise 0 to about 70%, morepreferably from about 20 to about 60%, by weight of the monomercomponent.

The monomer component utilized in the oil phase of the HIPEs may alsocomprise one or more monofunctional comonomers capable of impartingtoughness about equivalent to that provided by styrene to the resultingpolymeric foam structure. Tougher foams exhibit the ability to deformsubstantially without failure. These monofunctional comonomer types caninclude styrene-based comonomers (e.g., styrene and ethyl styrene) orother monomer types such as methyl methacrylate where the relatedhomopolymer is well known as exemplifying toughness. The preferredmonofunctional comonomer of this type is a styrene-based monomer withstyrene and ethyl styrene being the most preferred. The monofunctional"toughening" comonomer will normally comprise from about 0 to about 70%,preferably from about 20% to about 50%, most preferably from about 30%to about 50%, by weight of the monomer component.

In certain cases, the "toughening" comonomer can also impart the desiredrubber-like properties to the resultant polymer. For such comonomers,the amount that can be included in the monomer component will be that ofthe typical monomer and comonomer combined.

The monomer component contains a first (and optionally a second)polyfunctional crosslinking agent. As with the monofunctional monomersand comonomers, selection of the particular type and amount ofcrosslinking agent(s) is important to the realization of polymeric foamshaving the desired combination of structural and mechanical properties.It has also been found that such crosslinkers can advantageously containsilicon and/or germanium.

The first polyfunctional crosslinking agent can be selected frommonomers containing silicon and/or germanium. Generally, these comprisea relatively central silicon and/or germanium atom functionalized withat least two of the pendant reactive groups described hereinabove.Preferred examples have 3 or 4 pendant reactive groups are based onsilicon, though germanium can generally be substituted as well.Nonlimiting examples include tetraallyl silane (abbreviated "TAS"),tetrakis(2-methacryloxyethoxy)silane ("TKMES"),1,3-bis(3-methacryloxypropyl)tetramethyl-disiloxane ("BMPTDS"), and1,3,5-trivinyl-1,1,3,5,5-pentamethyltrisiloxane ("TVPTS"). Othernonlimiting examples include dimethoxydiallyl silane,bis(2-allyloxymethyl)-1-trimethylsiloxybutane,bis(methacryloxy)diphenylsilane, bis(methacryloxy)dimethyl silane,bis(4-styryl)dimethylsilane, diallyldiphenylsilane,diallyldimethylsilane, 1,3-diallyltetramethyldisiloxane,divinyltetramethyldisiloxane, hexavinyldisiloxane,bis(2-allyloxymethyl)phenethyl)-tetramethyldisiloxane,1,5-divinylhexamethyltrisiloxane, and tetraallyl germane. It has beenfound by experimentation that these crosslinkers can be used tostrengthen the polymer efficiently without unduly increasing the Tg ofthe polymer, which may not be disired in all cases. The polyfunctionalsilicon- or germanium-containing "crosslinking" comonomer will normallycomprise from about 5 to about 80%, preferably from about 10% to about60%, most preferably from about 25% to about 40%, by weight of themonomer component.

The first polyfunctional crosslinking agent can also be selected from awide variety of monomers containing two or more activated vinyl groups,such as divinylbenzenes and analogs thereof. Analogs of divinylbenzenesuseful herein include, but are not limited to, trivinyl benzenes,divinyltoluenes, divinylxylenes, divinylnaphthalenesdivinylalkylbenzenes, divinylphenanthrenes, divinylbiphenyls,divinyldiphenylmethanes, divinylbenzyls, divinylphenylethers,divinyldiphenylsulfides, divinylfurans, divinylsulfide, divinylsulfone,and mixtures thereof. Divinylbenzene is typically available as a mixturewith ethyl styrene in proportions of about 55:45. These proportions canbe modified so as to enrich the oil phase with one or the othercomponent. Generally, it is advantageous to enrich the mixture with theethyl styrene component while simultaneously reducing the amount ofstyrene in the monomer blend. The preferred ratio of divinylbenzene toethyl styrene is from about 30:70 to 55:45, most preferably from about35:65 to about 45:55. The inclusion of higher levels of ethyl styreneimparts the required toughness without increasing the Tg of theresulting copolymer to the degree that styrene does. This firstcross-linking agent can generally be included in the oil phase of theHIPE in an amount of from about 2 to about 50%, more preferably fromabout 10 to about 35%, most preferably from about 15% to about 25%, byweight of the monomer component (on a 100% basis).

The optional second crosslinking agent can be selected frompolyfunctional acrylates or methacrylates selected from the groupconsisting of diacrylates or dimethacrylates of diols and analogsthereof. Such crosslinking agents include methacrylates, acrylamides,methacrylamides, and mixtures thereof. These include di-, tri-, andtetra-acrylates, as well as di-, tri-, and tetra-methacrylates, di-,tri-, and tetra-acrylamides, as well as di-, tri-, andtetra-methacrylamides; and mixtures of these crosslinking agents.Suitable acrylate and methacrylate crosslinking agents can be derivedfrom diols, triols and tetraols that include 1,10-decanediol,1,8-octanediol, 1,6-hexanediol, 1,4-butanediol, 1,3-butanediol,1,4-but-2-enediol, ethylene glycol, diethylene glycol,trimethylolpropane, pentaerythritol, hydroquinone, catechol, resorcinol,trimethyl glycol, polyethylene glycol, sorbitol and the like. (Theacrylamide and methacrylamide crosslinking agents can be derived fromthe equivalent diamines, triamines and tetramines). The preferred diolshave at least 2, more preferably at least 4, most preferably 6, carbonatoms. This second cross-linking agent can generally be included in theoil phase of the HIPE in an amount of from 0 to about 15% by weight ofthe monomer component.

The major portion of the oil phase of the HIPEs will comprise theaforementioned monomers, comonomers and crosslinking agents. It isessential that these monomers, comonomers and crosslinking agents besubstantially water-insoluble so that they are primarily soluble in theoil phase and not the water phase. Use of such substantiallywater-insoluble monomers ensures that HIPEs of appropriatecharacteristics and stability will be realized. It is, of course, highlypreferred that the monomers, comonomers and crosslinking agents usedherein be of the type such that the resulting polymeric foam is suitablynon-toxic and appropriately chemically stable. These monomers,comonomers and cross-linking agents should preferably have little or notoxicity if present at very low residual concentrations duringpost-polymerization foam processing and/or use.

Another essential component of the oil phase of the HIPE is anemulsifier component that comprises at least a primary emulsifier.Suitable primary emulsifiers are well known to those skilled in the art.Particularly preferred emulsifiers include Span 20™, Span 40™, Span 60™,and Span 80™. These are nominally esters of sorbitan derived fromlauric, myristic, stearic, and oleic acids, respectively. Otherpreferred emulsifiers include the diglycerol esters derived frommonooleate, monomyristate, monopalmitate, and monoisostearate acids. Apreferred coemulsifier is ditallowdimethyl ammonium methyl sulfate.Mixtures of these emulsifiers are also particularly useful, as arepurified versions of each, specifically sorbitan esters containingminimal levels of isosorbide and polyol impurities.

When an optional secondary emulsifier(s) is included in the emulsifiercomponent, it is typically at a weight ratio of primary to secondaryemulsifier of from about 50:1 to about 1:4, preferably from about 30:1to about 2:1.

As is indicated, those skilled in the art will recognize that anysuitable emulsifier(s) can be used in the processes for making the foamsof the present invention. For examples, see U.S. Pat. No. 5,387,207 andU.S. Pat. No. 5,563,179.

The oil phase used to form the HIPEs comprises from about 80 to about98% by weight monomer component and from about 2 to about 20% by weightemulsifier component. Preferably, the oil phase will comprise from about90 to about 97% by weight monomer component and from about 3 to about10% by weight emulsifier component. The oil phase also can contain otheroptional components. One such optional component is an oil solublepolymerization initiator of the general type well known to those skilledin the art, such as described in U.S. Pat. No. 5,290,820 (Bass et al),issued Mar. 1, 1994, which is incorporated by reference.

A preferred optional component is an antioxidant such as a HinderedAmine Light Stabilizer (HALS) such asbis-(1,2,2,5,5-pentamethylpiperidinyl) sebacate (Tinuvin-765®) or aHindered Phenolic Stabilizer (HPS) such as Irganox-1076® andt-butylhydroxy-quinone. Another preferred optional component is aplasticizer such as dioctyl azelate, dioctyl sebacate or dioctyladipate. Yet another optional ingredient is filler particles which maytoughen the polymer and/or increase its thermal insulating properties.Example filler particules include aluminum, titanium dioxide, carbonblack, graphite, calcium carbonate, talc, and the like. Generally,particles which help make the polymer opaque in the infrared region arepreferred, such as carbon black and graphite. Other optional componentsinclude colorants (dyes or pigments), fluorescent agents, opacifyingagents, chain transfer agents, and the like.

2. Water Phase Components

The discontinuous water internal phase of the HIPE is generally anaqueous solution containing one or more dissolved components. Oneessential dissolved component of the water phase is a water-solubleelectrolyte. The dissolved electrolyte minimizes the tendency ofmonomers, comonomers, and crosslinkers that are primarily oil soluble toalso dissolve in the water phase. This, in turn, is believed to minimizethe extent to which polymeric material fills the cell windows at theoil/water interfaces formed by the water phase droplets duringpolymerization. Thus, the presence of electrolyte and the resultingionic strength of the water phase is believed to determine whether andto what degree the resulting preferred polymeric foams can beopen-celled.

Any electrolyte capable of imparting ionic strength to the water phasecan be used. Preferred electrolytes are mono-, di-, or trivalentinorganic salts such as the water-soluble halides, e.g., chlorides,nitrates and sulfates of alkali metals and alkaline earth metals.Examples include sodium chloride, calcium chloride, sodium sulfate andmagnesium sulfate. Calcium chloride is the most preferred for use inpreparing the HIPEs. Generally the electrolyte will be utilized in thewater phase of the HIPEs in a concentration in the range of from about0.2 to about 20% by weight of the water phase. More preferably, theelectrolyte will comprise from about 1 to about 10% by weight of thewater phase.

The HIPEs will also typically contain an effective amount of apolymerization initiator. Such an initiator component is generally addedto the water phase of the HIPEs and can be any conventionalwater-soluble free radical initiator. These include peroxygen compoundssuch as sodium, potassium and ammonium persulfates, hydrogen peroxide,sodium peracetate, sodium percarbonate and the like. Conventional redoxinitiator systems can also be used. Such systems are formed by combiningthe foregoing peroxygen compounds with reducing agents such as sodiumbisulfite, L-ascorbic acid or ferrous salts.

The initiator can be present at up to about 20 mole percent based on thetotal moles of polymerizable monomers present in the oil phase. Morepreferably, the initiator is present in an amount of from about 0.001 toabout 10 mole percent based on the total moles of polymerizable monomersin the oil phase.

3. Hydrophilizing Surfactants and Hydratable Salts

The polymer forming the HIPE foam structure will preferably besubstantially free of polar functional groups. This means the polymericfoam will be relatively hydrophobic in character. When these foams areto be used as insulating materials, resistance to water is generally adesired feature. Removal of the residual emulsifier and/or saltfollowing polymerization is generally desired in a manner described morefully hereafter.

B. Processing Conditions for Obtaining HIPE Foams

Foam preparation typically involves the steps of: 1) forming a stablehigh internal phase emulsifier (HIPE); 2) polymerizing/curing thisstable emulsion under conditions suitable for forming a solid polymericfoam structure; 3) optionally washing the solid polymeric foam structureto remove the original residual water phase, emulsifier, and salts fromthe polymeric foam structure; 4) thereafter dewatering this polymericfoam structure; and 5) optionally hydrophilizing the foam.

1. Formation of HIPE

The HIPE is formed by combining the oil and water phase components inthe previously specified ratios. The oil phase will typically containthe requisite monomers, comonomers, crosslinkers, and emulsifiers, aswell as optional components such as plasticizers, antioxidants, flameretardants, and chain transfer agents. The water phase will typicallycontain electrolytes and polymerization initiators.

The HIPE can be formed from the combined oil and water phases bysubjecting these combined phases to shear agitation. Shear agitation isgenerally applied to the extent and for a time period necessary to forma stable emulsion. Such a process can be conducted in either batchwiseor continuous fashion and is generally carried out under conditionssuitable for forming an emulsion where the water phase droplets aredispersed to such an extent that the resulting polymeric foam will havethe requisite structural characteristics. Emulsification of the oil andwater phase combination will frequently involve the use of a mixing oragitation device such as a pin impeller.

One preferred method of forming HIPE involves a continuous process thatcombines and emulsifies the requisite oil and water phase. In such aprocess, a liquid stream comprising the oil phase is formed.Concurrently, a separate liquid stream comprising the water phase isalso formed. The two separate streams are then combined in a suitablemixing chamber of zone such that the requisite water to oil phase weightratios previously specified are achieved.

In the mixing chamber or zone, the combined streams are generallysubjected to shear agitation provided, for example, by a pin impeller ofsuitable configuration and dimensions. Shear will typically be appliedto the combined oil/water phase stream at an appropriate rate. Onceformed, the stable liquid HIPE can then be withdrawn from the mixingchamber or zone. This preferred method for forming HIPEs via acontinuous process is described in greater detail in U.S. Pat. No.5,149,720 (DesMarais et al.), issued Sep. 22, 1992, which isincorporated by reference. See also copending U.S. application Ser. No.08/370,694, filed Jan. 10, 1995 by T. DesMarais (incorporated herein byreference), which describes an improved continuous process having arecirculation loop for the HIPE.

2. Polymerization/Curing of the HIPE

The HIPE formed will generally be formed, collected, or poured in asuitable reaction vessel, container or region to be polymerized orcured. In one embodiment, the reaction vessel is constructed ofpolyethylene from which the eventually polymerized/cured solid foammaterial can be easily removed for further processing afterpolymerization/curing has been carried out to the extent desired. Thetemperature at which the HIPE is poured into the vessel is generallyabout the same as the polymerization/curing temperature.

Suitable polymerization/curing conditions will vary depending upon themonomer and other makeup of the oil and water phases of the emulsion(especially the emulsifier systems used), and the type and amounts ofpolymerization initiators used. Frequently, however, suitablepolymerization/curing conditions will involve maintaining the HIPE atelevated temperatures above about 30° C., more preferably above about35° C., for a time period ranging from about 2 to about 64 hours, morepreferably from about 4 to about 48 hours. The HIPE can also be cured instages such as described in U.S. Pat. No. 5,189,070 (Brownscombe et al.)issued Feb. 23, 1993, which is herein incorporated by reference.

A porous water-filled open-celled HIPE foam is typically obtained afterpolymerization/curing in a reaction vessel, such as a cup or tub. Thispolymerized HIPE foam is typically cut or sliced into a sheet-like form.Sheets of polymerized HIPE foam are easier to process during subsequenttreating/washing and dewatering steps, as well as to prepare the HIPEfoam for use in insulation materials. The polymerized HIPE foam istypically cut/sliced to provide a cut thickness in the range of fromabout 0.08 in. to about 3.5 in.

3. Treating/Washing HIPE Foam

The polymerized HIPE foam formed will generally be filled with residualwater phase material used to prepare the HIPE. This residual water phasematerial (generally an aqueous solution of electrolyte, residualemulsifier, and polymerization initiator) may be removed prior tofurther processing and use of the foam. Removal of this original waterphase material will usually be carried out by compressing the foamstructure to squeeze out residual liquid and/or by washing the foamstructure with water or other aqueous washing solutions. Frequently,several compressing and washing steps, e.g., from 2 to 4 cycles, will bedesirable. It is preferable that the water used in these washing beheated to at least about the Tg of the polymer so as to maintain itsflexibility and compliance during compressive dewatering and to reduceand prevent damage to the foam structure.

4. Foam Dewatering

After the HIPE foam has been treated/washed, it will be dewatered.Dewatering can be achieved by compressing the foam to squeeze outresidual water, by subjecting the foam or the water therein totemperatures of from about 60° to about 200° C. or to microwavetreatment, by vacuum dewatering or by a combination of compression andthermal drying/microwave/vacuum dewatering techniques. These HIPE foamsare typically compressively dewatered to a thickness of about 1/3 (33%)or less of their fully expanded thickness. The dewatering step willgenerally be carried out until the HIPE foam is ready for use and is asdry as practicable. Frequently such compression dewatered foams willhave a water (moisture) content of from about 1% to about 15%, morepreferably from about 5% to about 10% by weight on a dry weight basis.

5. Foam Hydrophilization

When hydrophilic foams are desired (e.g., for use in absorbentarticles), it may be desirable to treat the washed, dewatered foam witha hydrophilizing agent. Suitable hydrophilizings agents and methods forhydrophilizing foams are disclosed fully at, e.g., column 22 to column24 of U.S. Pat. No. 5,387,207.

IV. Test Methods

Samples are prepared for evaluation by slicing into 3 to 8 mm thickpieces and stamping out of these pieces cylinders having a diameter of2.54 cm. These cylinders or "pucks" are washed successively in water(with intermediate squeezing steps) and 2-propanol to remove residualsalt and emulsifier. These samples are then dried (either at ambient orelevated temperatures up to 65° C.). In some cases, the samples collapseupon drying and must be freeze-dried to recover a fully-expanded samplefor testing.

A. Dynamic Mechanical Analysis (DMA)

DMA is used to determined the Tgs of polymers including polymeric foams.The sample pucks are analyzed using a Rhemometrics RSA-II dynamicmechanical analyzer set in compression mode using parallel plates 25 mmin diameter. Instrument parameters used are as follows:

Temperature step from ca. 120° C. to -50° C. in steps of 1.0° to 2.5°C., depending on the precision needed to define the transition point

Soak intervals between temperature changes of 120-160 seconds

Dynamic strain set at 0.7%

Frequently set at 1.0 radians/second

Autotension set in static force tracking dynamic force mode with initialstatic force set at 5 g.

The glass transition temperature is taken as the maximum point of theloss tangent (tan[δ]) versus temperature curve.

B. Yield Stress

Yield stress can be quantified by compressing a foam sample at aspecific rate and at a specific temperature and measuring the resistanceexerted by that sample to the compression. Typically, the data areformatted as a plot of stress on the y-axis and strain on the x-axis.Such plots typically show an initial linear response followed by a rapidloss in resistance to further compression at a point termed the "yieldpoint". The yield point is defined as the intersection of the linesformed by the linear regions before and after the yield point. The yieldstress is the stress value at that intersection. The analysis isperformed using the same equipment defined in the preceding section(Rheometrics RSA-II) operating in a constant strain mode. In this mode,the temperature is set to 31° C. and the strain rate is set at 0.1%second. The sample is held at this temperature for at least 5 minutesprior to the initiation of compression to bring it to the definedtemperature. The experiment is run for 10 minutes in compressionfollowed by 10 minutes at the same rate of strain in the reversedirection. The data analysis is conducted as described above.

C. Density

Density is the weight of a given sample divided by its volume and may bedetermined by an appropriate standard method. Density measurements usedherein involved weighing the cylindrical samples (pucks) used in theabove measurements which had a diameter of 2.54 cm. The thickness of thesample was determined by measurement. The density was then calculatedusing the equation density=weight (mg)/(0.057×thickness (mm) expressedin units of mg/cc. The samples were typically washed in water and2-propanol to remove salt and residual emulsifier from the sample priorto these measurements. The measured densities conformed closely to whatis expected from the water-to-oil ratio of the HIPE from which theparticular foam was derived, e.g., density=(1/(W:O ratio+1)) in units ofg/cc.

V. Specific Examples

The following examples illustrate the preparation of HIPE foams usefulin the present invention.

EXAMPLES 1-5 Preparation of Foams from HIPEs

Examples 1-5 are illustrative of low density having desirably low Tgsand desirably high yield stresses achieved by using a silicon-containingTg lowering comonomer.

A) HIPE Preparation

The water phase is prepared consisting of 10% calcium chloride(anhydrous) and 0.05% potassium persulfate (initiator).

The oil phase is prepared according to the monomer ratios described inTable 1, all of which include an emulsifier for forming the HIPE. Thepreferred emulsifier used in these examples is diglycerol monooleate(DGMO) used at a level of 5-10% by weight of oil phase. The DGMOemulsifier (Grindsted Products; Brabrand, Denmark) comprisesapproximately 81% diglycerol monooleate, 1% other diglycerol monoesters,3% polyglycerols, and 15% other polyglycerol esters, imparts a minimumoil phase/water phase interfacial tension value of approximately 2.5dyne/cm and has a critical aggregation concentration of approximately2.9 wt %.

To form the HIPE, the oil phase is placed in a 3" diameter plastic cup.The water phase is placed in a jacketed addition funnel held at about50° C. The contents of the plastic cup are stirred using a Cafrano RZR50stirrer equipment with a six-bladed stirrer rotating at about 300 rpm(adjustable by operator as needed). At an addition rate sufficient toadd the water phase in a period of about 2 to 5 minutes, the water phaseis added to the plastic cup with constant stirring. The cup is moved upand down as needed to stir the HIPE as it forms so as to incorporate allthe water phase into the emulsion.

B) Polymerization/Curing of HIPE

The HIPE in the 3" plastic caps are capped and placed in an oven set at65° C. overnight to cure and provide a polymeric HIPE foam.

C) Foam Washing and Dewatering

The cured HIPE foam is removed from the cup as a cylinder 3" in diameterand about 4" in length. The foam at this point has residual water phase(containing dissolved emulsifiers, electrolyte, initiator residues, andinitiator) about 50-60 times (50-60×) the weight of polymerizedmonomers. The foam is sliced on a meat slicer to give circular piecesabout 3 to about 8 mm in thickness. These pieces are washed in distilledwater and compressed to remove the water 3 to 4 times. They are furtherwashed in 2-propanol and compressed about 3 to 4 times. The pieces arethen dried in an oven at 65° C. for 1 to 2 hours. In some cases, thefoams collapse upon drying and must be freeze-dried from the waterswollen state to recover fully expanded foams. Various shapes and sizesof foams may be prepared similarly by use of appropriately shapedvessels in which the HIPE is cured and/or appropriate cutting orshaping. The process for preparing the foams of the present inventionmay also be a continuous one, such as that described in U.S. Pat. No.5,149,720, issued Sep. 22, 1992 to DesMarais et al. or copending U.S.patent application Ser. No. 08/370,694, filed by DesMarais on Jan. 10,1995, the disclosure of each of which is incorporated by reference.

Specific nonlimiting examples of combinations of comonomers to makefoams of the present invention are shown in Tables 1 and 2.

                  TABLE 1                                                         ______________________________________                                        Foam Composition and Properties.                                                                       Silicon- Yield                                            containing Stress Density Tg                                               Example #   EHA %  DVB % monomer (%) (psi) (mg/cc) (° C.)            ______________________________________                                        1      55%     40%     AETMS, 5%                                                                              0.59  16    25°                          2       50%    40%    AETMS, 10%     0.72      20      22°                                                        3       50%    40%    APTMS,                                                 10%     0.90      18                                                          18°                          4       40%    40%    APTMS, 20%     0.79      15      24°                                                        5       30%    40%    APTMS,                                                 30%     0.68      15                                                          23°                        ______________________________________                                         EHA = 2ethylhexyl acrylate; available from Aldrich Chemical Corp of           Milwaukee, WI.                                                                DVB = divinyl benzene, based on 39-42% purity with 58-61% ethyl styrene       impurity; available from Dow Chemical Corp. of Midland, MI.                   AETMS = 2(acryloxyethoxy)trimethylsilane.                                     APTMS = (3acryloxypropyl)methylbis-(trimethylsiloxy)silane.              

All silicon and germanium compounds used herein were obtained fromGelset, Inc. of Tullytown, Pa. unless otherwise noted.

EXAMPLES 6-14

Examples 6-14 are illustrative of low density foams having desirably lowTgs and high yield stresses achieved by using a polyfunctionalsilicon-containing crosslinking agent. The foams are prepared using theprocess described for making foams of Examples 1-5, and the oil phasecomponents described in Table 2.

                  TABLE 2                                                         ______________________________________                                        Foam Composition and Properties.                                                Ex-                      Silicon-  Yield                                      ample EHA DVB ISO containing Stress Density Tg                                #   %  % % monomer (%) (psi) (mg/cc) (° C.)                          ______________________________________                                        6     55%    33%    0%   BMAPTD, 12%                                                                             0.44 18    19°                        7      55%  33%    0%     TUPMTS, 12%            0.58    16                                                               14°                        8      55%  33%    0%      TAS, 12%              0.77    17                                                               16°                        9      55%  33%    0%     TKMES, 12%             0.90    17                                                               26°                        10     50%  33%    0%     TKMES, 17%             1.43    16                                                               54°                        11     55%  38%    0%     TKMES, 7%              0.71    16                                                               33°                        12     55%  28%    0%     TKMES, 17%             0.96    17                                                               23°                        13      0%   33%    55%    TKMES, 12%             1.68    13                ______________________________________                                                                                      NM                               ISO = isoprene; available from Aldrich Chemical Corp. Because isoprene        boils at 33° C., the HIPE preparation for Example 13 is carried ou     at 0-5° C. and the container is cured in a pressure vessel             pressurized to 30 psi with argon. The pressure vessel is placed in the        curing oven set at 65° C. for two days to effect curing.               BMAPTD = 1,3bis(3-methylacryloxypropyl)tetramethyldisiloxane.                 TUPMTS = 1,3,5trivinyl-1,1,3,5,5-pentamethyltrisiloxane.                      TAS = tetraallyl silane.                                                      TKMES = tetrakis(methacryloxyethoxy)silane.                                   NM = Not Measured                                                        

All silicon and germanium compounds used herein are obtained fromGelset, Inc. of Tullytown, Pa. unless otherwise noted.

In other examples, other alkyl acrylates are used in partial or totalsubstitution for EHA, other crosslinkers are used in partial or totalsubstitution for DVB, related analogs are used wherein germanium is usedin partial or total substitution for silicon, and other emulsifiersincluding ditallowdimethylamonium methylsulfate are used in partial ortotal substitution for DGMO, as described hereinabove.

What is claimed is:
 1. A polymeric foam material comprising at least 5%based on the weight of the foam, of one or more comonomer(s) selectedfrom the group consisting of silicon-containing comonomers,germanium-containing comonomers, and mixtures thereof; characterized inthat the polymeric foam materials has:A) a density of less than 0.10g/cc; B) a glass transition temperature (Tg) of from -40° to 90° C.; andC) a yield stress value at least 0.25 psi.
 2. The polymeric foammaterial of claim 1 wherein the foam comprises from about 8% to about50%, based on the total weight of the foam, of one or more comonomers(s)selected from the group consisting of silicon-containing comonomers,germanium-containing comonomers, and mixtures thereof.
 3. The polymericfoam of claim 1 wherein the foam is hydrophilic and is capable ofacquiring and distributing aqueous fluids.
 4. The polymeric foammaterial of claim 3 wherein the foam has a specific surface area of atleast about 0.01 m² /cc.
 5. The polymeric foam material of claim 4wherein the foam has a specific surface area of at least about 0.025 m²/cc.
 6. The polymeric foam material of claim 3 wherein the foam has a Tgof from about 15° to about 50° C.
 7. The polymeric foam material ofclaim 3 wherein the foam has a yield stress value of at least about 0.25psi.
 8. The polymeric foam material of claim 7 wherein the foam has ayield stress value of at least about 0.50 psi.
 9. The polymeric foammaterial of claim 3 wherein the foam has an average cell size of notmore than about 150 μm.
 10. The polymeric foam material of claim 1wherein the foam is hydrophobic.
 11. The polymeric foam material ofclaim 10 wherein the foam has an average cell size of from about 10 μmto about 100 μm.
 12. The polymeric foam material of claim 11 wherein thefoam has an average cell size of from about 15 μm to about 35 μm. 13.The polymeric foam material of claim 10 wherein the foam has a Tg offrom about 15° to about 50° C.
 14. A polymeric foam material obtainedfrom polymerizing a high internal phase water-in-oil emulsion, whereinthe foam comprises at least about 5%, based on the weight of the foam,of one or more comonomer(s) selected from the group consisting ofsilicon-containing comonomers, germanium-containing comonomers, andmixtures thereof.
 15. The polymeric foam material of claim 14 whereinthe foam comprises from about 8% to about 50%, based on the total weightof the foam, of one or more comonomer(s) selected from the groupconsisting of silicon-containing comonomers, germanium-containingcomonomers, and mixtures thereof.
 16. The polymeric foam of claim 14wherein the foam is hydrophilic and is capable of acquiring anddistributing aqueous fluids.
 17. The polymeric foam of claim 14 whereinthe foam is hydrophobic.
 18. The polymeric foam of claim 1 wherein thefoam is prepared by the process comprising the steps of:(A) forming awater-in-oil emulsion under low shear mixing from:(1) an oil phasecomprising:(a) from about 80% to about 98% by weight of a monomercomponent capable of forming a copolymer having a Tg value of from about-40° C. to about 90° C., said monomer component comprising:(i) at leastabout 5% by weight of a material selected from the group consisting ofone or more comonomers containing silicon, one or more comonomerscontaining germanium, and mixtures thereof; (ii) from about 0% to about70% by weight of a substantially water-insoluble, monofunctional monomercapable of forming a homopolymer having a Tg of about 40° C. or less;(iii) from about 0% to about 70% by weight of a substantiallywater-insoluble, monofunctional comonomer capable of imparting toughnessabout equivalent to that provided by styrene; (iv) from about 0% toabout 50% of a first substantially water-insoluble, polyfunctionalcrosslinking agent selected from the group consisting of divinyl benzeneand analogs thereof; and (v) from about 0% to about 15% of a secondsubstantially water-insoluble, polyfunctional crosslinking agentselected from the group consisting of diacrylates and dimethacrylates ofdiols and analogs thereof; and (b) from about 2% to about 20% by weightof an emulsifier component which is soluble in the oil phase and whichis suitable for forming a stable water-in-oil emulsion; (2) a waterphase comprising from about 0.1% to about 20% by weight of awater-soluble electrolyte; and (3) a volume to weight ratio of waterphase to oil phase of at least about 10:1; and (B) polymerizing themonomer component in the oil phase of the water-in-oil emulsion to formthe polymeric foam material.
 19. The polymeric foam of claim 18, whereinthe monomer component of the oil phase of the emulsion comprises fromabout 8 to about 50% of a material selected from the group consisting ofone or more monofunctional comonomers comprising silicon, one or moremonofunctional comonomers comprising germanium, and mixtures thereof.20. The polymeric foam of claim 19, wherein the monomer component of theoil phase of the emulsion comprises a comonomer selected from the groupconsisting of (3-acryloxypropyl)methylbis-(trimethylsiloxy)silane,allyltriisopropyl silane, allyltriphenyl silane,bis(trimethylsilyl)itaconate, p-(t-butyldimethylsiloxy)styrene,methacrylamido-propyltriethoxysilane, methacryloxyethoxytrimethylsilane,(methacryloxymethyl)-dimethylethoxysilane, methacryloxytrimethyl silane,(2,4-pentadienyl)trimethylsilane, styrylethyltrimethoxysilane,3-(N-styrylmethyl-2-aminoethylamino)propyltrimethoxy-silanehydrochloride, (m,p-vinylbenzyloxy)trimethylsilane, vinyltrimethylsilane, vinyldimethylethyl silane, vinylpentamethyldisiloxane, vinyltrifluoromethyldimethyl silane, vinyltris(trimethylsiloxy)silane,vinyltriethyl germane, and mixtures thereof.
 21. The polymeric foam ofclaim 18 wherein the monomer component of the oil phase of the emulsioncomprises from about 20 to about 60% by weight of a non-silicon,non-germanium containing monofunctional monomer capable of forming ahomopolymer having a Tg of about 40° C. or less.
 22. The polymeric foamof claim 18 wherein the monomer component of the oil phase of theemulsion comprises from about 5 to about 80% by weight of apolyfunctional crosslinker that comprises silicon or germanium.
 23. Thepolymeric foam of claim 22 wherein the polyfunctional crosslinker isselected from the group consisting of tetraallyl silane,tetrakis(2-methacryloxyethoxy)silane,1,3-bis(3-methacryloxypropyl)tetramethyl-disiloxane,1,3,5-trivinyl-1,1,3,5,5-pentamethyltri-siloxane, dimethoxydiallylsilane, bis(2-allyloxymethyl)-1-trimethylsiloxybutane,bis(methacryloxy)diphenylsilane, bis(methacryloxy)dimethyl silane,bis(4-styryl)dimethy-lsilane, diallyldiphenylsilane,diallyldimethylsilane, 1,3-diallyltetramethyldisiloxane,divinyltetramethyldisiloxane, hexavinyldisiloxane,bis(2-allyloxymethyl)phenethyl)-tetramethyldisiloxane,1,5-divinylhexamethyltrisiloxane, tetraallyl germane, and mixturesthereof.
 24. The polymeric foam of claim 22 wherein the monomercomponent of the oil phase of the emulsion comprises from about 10% toabout 35% by weight of a polyfunctional crosslinking agent selected fromthe group consisting of divinyl benzene and analogs thereof.